Optical sensor and method for detecting projectile impact location and velocity vector

ABSTRACT

An optical sensor and method for detecting a projectile velocity vector includes optically detecting the arrival of a projectile. The sensor includes a sandwich of a transparent layer within two reflective layers, which in turn are within two opaque layers. An optical sensor structure includes a set of sensors positioned in respective planes, wherein at least two non-parallel optical sensors are used for each trajectory dimension of interest that differs from the primary direction of motion of the projectile and one additional optical sensor may be used for independent measurement of velocity attenuation. An optical sensor structure includes a set of sensors positioned in respective planes, wherein at least two of the optical sensors are oriented in respective planes that are parallel and potentially offset from each other. A tiling of the optical sensors or optical structures is also possible.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.60/343,724, filed on Oct. 25, 2001, which is hereby incorporated byreference in its entirety.

STATEMENT OF GOVERNMENTAL INTEREST

This invention was made with U.S. Government support under Navy contractno. N00024-98-D-8124. The U.S. Government has certain rights in theinvention.

BACKGROUND OF THE INVENTION

The present invention relates to sensors and in particular to opticalsensors. There are both electrical and optical sensors capable ofsensing pressure, stress, and penetration of objects. However, presentelectrical penetration sensors detect penetration of the sensor by aprojectile via electrical shorts in the sensor. The penetratingprojectile creates the short between two separated conductive layers.This short can be sensed and used to identify a penetration. One of thedrawbacks of electrical sensors is the problem of inadvertent shorts ofthe two separated conductive layers. The conductive layers must beinsulated from each other and the other conductive parts of the sensorand from the structure on which the sensor is mounted. This adds to thedesign, installation, and the overall troubleshooting and maintenancecosts of the sensor. Electrical sensors can also generate inadvertentsparks, which in some applications, where explosives might be nearby, ishighly undesirable. Electrical sensors are also subject to electricalnoise that is generated from electromagnetic interference. Manysituations where the detection of penetration is desirable are locatedclose to highly explosive events, which events have been know togenerate electrical noise. Noisy electrical signals can be difficult tointerpret and can cause erroneous indication of penetration events.Another drawback of using electrical sensors is that the passingprojectile can short out the signal cable. This event can erroneously beinterpreted as a penetration event at the sensor or, even worse, shortout the power supply and cause erroneous readings on other sensors thatare connected to the same system. Electrical sensors have also proven tobe susceptible to chemicals, which limits their applications.

Current optical sensors are not subject to the shorting problem. Forexample, ITT Industries, Advanced Engineering & Sciences of Reston, Va.offers a Photonic Hit Indicator. That sensor includes a grid of opticalfibers. A projectile that penetrates the sensor cuts some of the opticalfibers. Detection of the loss of optical signal in the severed fiber isused to identify the location of the projectile's penetration. Thissensor is, however, an active sensor. That is, it requires light to beapplied to the optical fibers of the sensor. Severing of the opticalfibers by the penetrating projectile prevents the applied light fromreaching photodetectors. Detecting the absence of the applied light onthe optical fiber of the grid provides an indication of where theprojectile penetrated the sensor. One disadvantage of this type ofsensor is that a fine and precise layout of many optical elements isneeded to achieve a fine spatial resolution of the impact point. Inaddition, such active layouts of optical fibers are expensive tomanufacture. Also, like electrical sensors, they require power to drivethe light source or sources for the optical fibers or fibers.

The prior art sensors discussed above provide for penetration time andlocation. They do not directly provide additional details on thetrajectory of the projectile or other penetration characteristics of theprojectile. In addition, both methods discussed above degradesignificantly as projectile damage accumulates in multiple projectilescenarios. In the case of the electrical detection panels, a penetratingfragment will often leave the panel shorted out. Once a panel isshorted, it cannot detect the penetration of subsequent projectiles. Inthe case of the Photonic hit indicator, once a projectile penetrates, itcreates blind spots at other locations where the same optical fibersrun; each optical element is only capable of registering the firstprojectile passing through.

There are other systems that employ high-speed imaging to measureprojectile trajectories. These systems are expensive to purchase andoperate and are limited in use to very specific applications.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an inexpensiveoptical sensor.

It is a further object of the present invention to provide an opticalsensor that does not require power.

It is another object of the present invention to provide an opticalsensor that does not require an external light source.

It is still a further object of the present invention to provide anoptical sensor structure for detecting the speed and direction of aprojectile.

It is still a further object of the present invention to provide anoptical sensor structure for detecting the impact location of aprojectile.

It is still another object of the present invention to provide a passiveoptical sensor structure for detecting the speed and direction of aprojectile.

It is still another object of the present invention to provide a passiveoptical sensor structure for detecting the impact location of aprojectile.

It is still another object of the present invention to provide a passiveoptical sensor structure for reliably detecting the trajectory of morethan one projectile in succession.

It is still another object of the present invention to provide a passiveoptical sensor structure for detecting multiple nearly simultaneoustrajectories of projectiles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded schematic representation of an optical sensorembodying the present invention.

FIG. 2 is a schematic representation of an optical sensor structureembodying the present invention.

FIG. 3 is a schematic representation of the FIG. 2 optical sensorstructure viewed along the XY plane.

FIG. 4 is a schematic representation of the FIG. 2 optical sensorstructure viewed along the XZ plane.

FIG. 5 is a schematic block diagram of a detection system embodying thepresent invention with a single optical fiber transmitting an opticalsignal from each optical sensor to a corresponding detector.

FIG. 6 is a schematic block diagram of a detection system embodying thepresent invention with a single optical fiber transmitting all opticalsensor signals to a single detector.

FIG. 7 is a schematic block diagram of a detection system embodying thepresent invention with a single optical fiber transmitting all opticalsensor signals to an array of detectors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an exploded schematic representation of an optical sensorembodying the present invention. In FIG. 1, reference numerals 10 and 30identify opaque layers. These layers shield a light generator layer (15,20, 25) from ambient light. The composition of the opaque layers dependsupon the sensor application and the expected ambient light. Someexemplary materials that can be used in the opaque layers 10 and 30include, but are not limited to, optically opaque plastics such aspolycarbonates (e.g., Lexan®) and acrylics (e.g., Plexiglas®),structural fiber reinforced composites, metals (e.g., copper), andsilicone molding compounds. In the exemplary embodiment shown in FIG. 1,the light generator layer (15, 20, 25) includes reflective layers 15 and25, together with a transparent layer 20.

The reflective layers 15 and 25 can comprise, for example, opticallyreflective plastics such as mirrored polycarbonate (e.g., Lexan®) andacrylic (e.g., Plexiglass®), metal alloy films (e.g., aluminizedpolyimide-based Kapton®), and highly polished metals. In an exemplaryembodiment, the transparent layer 20 can comprise, for example,optically clear plastics such as polycarbonates (e.g., Lexan®) andacrylics (e.g., Plexiglass®) and silicone-based molding compounds suchas conformable gels. The transparent layer can also comprise a gas, suchas, for example, air, or nitrogen. However, if using a gas for thetransparent layer 20, the light sensed by the fiber optic 35, would beprimarily generated by a projectile passing through reflective layers 15and 25 and some portion of the transparent layer may require additionalsolid supports to maintain the structure.

In general, the optical sensor shown in exploded form in FIG. 1, is astack of materials designed to provide an optical pulse to the opticalfiber, 35, when a sufficiently energized projectile hits and/orpenetrates the stack. The optical sensor of the present invention isgenerally planar. The layers of the sensor are planar in that they havea generally constant thickness along the length and width dimensions ofthe sensor. They can be constructed to be flexible and to conform to adesired structure of interest while substantially maintaining thethickness of the sensor layers along the length and width dimensions ofthe sensor. The sensor layers can be cut and/or machined to matchpre-existing surfaces. The purpose the optical sensor of the presentinvention is to provide the time of passage of a projectile through thelight generator layer to some external measurement system that iscapable of converting the optical pulse into electronic form for storageand/or processing. The value of the information contained within thegenerated light pulse is specific to each application. The spatialresolution of detection for single element optical sensors of thepresent invention corresponds to the area of the sensor. The temporalresolution of the measurement is determined by the rate at which theoptical fiber is sampled. Since the optical sensor of the presentinvention is passive, it is intrinsically safe for use in explosiveenvironments and immune to electromagnetic interference.

FIG. 2 is a schematic representation of an optical sensor structureembodying the optical sensor of the present invention. By using multipleoptical sensors in accordance with the present invention in a suitablegeometrical arrangement, additional information regarding the nature ofthe projectile can be obtained. FIG. 2 schematically illustrates anexemplary one of such suitable geometrical arrangements. By employingthe exemplary geometric arrangement shown in FIG. 2, additionalinformation that can be computed includes: (1) the penetration locationof the projectile on the face of the panel; (2) the three spatialcomponents of projectile velocity; and (3) the speed attenuation factorof the projectile.

An example method for computing (1), (2), and (3) is shown in theexemplary MATLAB code listing below. The velocity attenuation factor (R)of a projectile pertains to the manner in which the projectile losesenergy as it passes through the layers of the optical sensors. For agiven optical layer, R is defined as the ratio of Vin to Vout, that is,the velocity upon reaching the plane and the velocity upon leaving theplane. For a given optical sensor structure, the velocity attenuationthat occurs during the passage through each optical sensor layer is afunction of the projectile velocity and size and the composition of theoptical sensor structure layers. Since the optical sensor structure candetect the time at which a projectile reaches a given layer of thestructure, the times can be used to measure the projectile velocityattenuation factor R It is also possible to characterize variousprojectiles by using this additional information. The FIG. 2 structureincludes seven optical sensors positioned in seven planes (40, 50, 55,60, 65, 70, and 45). The optical sensors can be of the type shown inFIG. 1, but are not limited to such sensors. The use of a seventhoptical plane (45) in the structure allows for an independent measure ofthe velocity attenuation R. In the absence of this plane, R must beassumed and significant error can occur in the computation of theprojectile parameters. If R is not equal to unity, then the mathematicsof computing the projectile trajectory is more complicated, since thevelocity will change in a step-wise manner as it penetrates the layersof the optical sensor structure. Because the projectile velocityattenuates as it passes through the optical structure, the measuredtimes corresponding to when the projectile passes each plane should bemodified in a specific way prior to the computation of the projectileparameters. The addition of the seventh plane (45) allows for thecomputation of R. The computation of R then allows the measuredpenetration times to be corrected for what they would have been if novelocity attenuation had occurred. While the use of the attenuationfactor, R, complicates the computational steps, the independentmeasurement of R provides for a much more accurate trajectoryreconstruction. The basic logic is reflected in the exemplary MATLABcode below. The attenuation factor, R, is computed by finding the realroot of a fifth order polynomial. Then a matrix is constructed tocontract the measured penetration times to what they would have been ifR had been unity. The contracted time vector is then used to compute theprojectile parameters.

If the initiation time of the projectile motion is also known ormeasured, then the original location of the projectile at the initiationtime can be computed. It is not necessary that the original location isin front the first plane, 40. It can just as well be beyond the lastplane, 45. This process is also reflected in the exemplary MATLAB codelisting below. If the initiation time measurement is in error, then thecomputed projectile velocities will still be accurate but the computedinitial location will be in error.

If the origination position of a projectile is desired, then theinitiation time is needed to determine that position. The measurement ofinitiation time may be performed differently for different applications.In the case of a bright flash in close proximity, an optical pickupfiber or a photodiode can be used. If an optical fiber is used, it canbe attached to the optical sensor structure. The optical fiber shouldhave a large numerical aperture to be able to receive light from manydirections. The end of the fiber should be oriented in the expectedlocation of the origination flash. If it is unknown apriori whether theorigination flash will occur in front of or behind the sensor structure,then two optical fibers may be used, one looking aft and one lookingforward. The two optical fibers may then be joined into one at a 2-to-1optical coupler. The exemplary MATLAB code uses the parameter t_mark asthe initiation time of the projectile. The exemplary code processes thetemporal signals with t=0 defining the time when the projectilepenetrates first plane, 40. Therefore, t_mark may in fact be negative.If a data system is used that sets t=0 as the initiation time of theprojectile. The times need to be shifted so that the penetration of thefirst plane corresponds to t=0 prior to using the exemplary MATLAB codeas is. Care should be exercised if using this approach to ensure thatthe response time of the initiation detection is minimal. In the case ofa more distant flash with audible report from, for example, a bullet,the computation of initiation time would use the local temperature andpressure to compute the sound speed first. This allows for the time thatit takes the sound to travel to the audible sensor from the projectilemotion-initiating event, such as an explosion or gun firing. The timethat the projectile arrives at each layer of the optical sensorstructure shown in FIG. 2 is detected via the light pulse generated ineach corresponding layer of the structure. These times can be used tocompute the three spatial components of the projectile velocity, theimpact location, and the speed attenuation factor. With the projectilevelocity and the sound speed both known quantities, the initiation timeof the projectile motion can then be computed since the distance thatthe sound travels and the distance that the projectile travels are ofcourse equal.

Referring to FIG. 2, if simultaneous arrival of multiple projectileswith differing trajectories at the structure occurs, then the opticalsignals produced by the structure can be quite complex. The ability toresolve multiple projectiles is dependent on the particularcircumstances. Generally, the multiple projectiles are still resolvableas long as the optical signal from one does not mask the optical signalfrom another. Masking can occur if two fragments pass through the sameplane simultaneously. In some cases, it is possible to resolve multipletrajectories even if limited masking occurs, since the absence of someportions of one trajectory could indicate when the masked signal wouldhave had to have been generated. It is advantageous to keep the opticalpulse width that is generated by each penetration as narrow as possibleto limit masking as long as the data acquisition system is capable ofresolving it. The pulse width can be reduced by adding thermallyconductive material to the light generator layer. Such materials mightinclude diamond or metallic thin films or particulates. This reduces thepulse width by rapidly dispersing the heat that is generated duringpenetration. Photochromic dyes and polymers can also be used to reducethe pulse width. These materials work by reducing opticaltransmissibility as the signal intensity rises. If multiple projectilepenetrations occur, the penetration times associated with eachprojectile must be separated prior to using the exemplary MATLAB code.The system configuration can be simplified by using multiple planarelements that are connected to a single optical fiber through a 7-to-1optical connector (such as schematically shown as element 155 in FIG.6), rather than each optical sensor layer having its own optical fiberconnected thereto as schematically shown in FIG. 5. Thus, only one fiberhas to transmit the optical signal to the associated computer forprocessing in accordance with, for example, the exemplary MATLAB codeshown below. It will be understood by those skilled in the art that theexemplary MATLAB code is just that, an example. The invention is notrestricted to any given implementation, and can obviously be implementedin a variety of different procedures. One way to use the 7-to-1 opticalconnector and still be able to resolve multiple penetrations is tospectrally modify the light generated by each layer. This can beaccomplished by doping the transparent or reflective layers to tailorthe wavelength band that enters the fiber for each plane. The opticalfiltering could alternatively be performed by using optical filters atthe 7-to-1 optical connector. If this technique is used, then sevenindependent detector channels would be used on the receiving end, eachof which is designed to respond to a particular wavelength, such asschematically shown in FIG. 7.

If only one optical fiber is used together with, for example, the 7-to-1optical connector, then the relaxation time from a single penetrationshould be less than the inter-panel transit time within the opticalsensor structure. This can be realized by choosing materials thatrapidly distribute the heat generated when a projectile passes throughor alternatively by using special optical materials that reduce opticaltransmissibility as the intensity rises. Examples of such materials thatexhibit photochromic characteristics include silver halide, tungstenoxide, titanium dioxide and other photochromic dyes and polymers. Inaddition, exemplary heat-dissipative materials could include diamond ormetallic films or particulates. As long as the photodiode that isoperatively coupled to the fiber optic does not saturate, an AC coupledfiltering circuit can also be used to improve the ability to resolve apenetration at a particular optical sensor layer at a particular timewithin the optical sensor structure. The use of AC coupled filteringcircuits effectively extends the dynamic range of the detectors.

The exemplary embodiment of an optical sensor structure shown in FIG. 2includes 21 elements. It includes seven optical sensors (40, 50, 55, 60,65, 70, and 45) positioned in respective planes. These optical sensorsare identified with the reference letter (P). The exemplary FIG. 2structure also includes six rectangular spacer panels, and eighttriangular wedge panels. These elements are not shown in FIG. 2, but areshown in FIGS. 3 and 4.

In FIGS. 3 and 4, the spacers are identified with the reference letter(S), and the wedges are identified with the reference letter (W). InFIGS. 3 and 4, two of the eight wedges are not visible in the particularperspective shown in the respective figures. The stack-up of the opticalsensor structure illustrated in FIG. 3 in the X dimension isPSWPWSWPWSWPWSWPWSPSP. Obviously, the orientation of the wedges dependson the optical sensor layer that it is positioning.

Referring to FIG. 2, the end optical sensor layers, 40 and 45, have thedimensions of L×L×S, where L denotes the length and width of each layer,and S is the thickness of the layer. This example uses a square layer,but the shape can be any geometrical shape. The five internal opticalsensor layers (50, 55, 60, 65 and 70) are rectangles that, in theillustrated example, have dimensions determined by the tilt parameter D.In the exemplary embodiment discussed herein, the tilt parameter, D, isequal to the arc tangent of the wedge angle A shown in FIG. 3. Thedimensions of the interior panels are L×Lsec(A)×S, where Lsec(A) is Ltimes the secant of the angle A. In the illustrated example, all wedgeelements are identical, and all spacer elements are identical. If theseelements are not identical, the calculations illustrated in the MATLABcode below must be adjusted to account for the different shapes. Thespacer elements are rectangular and the dimensions are L×L×(H−S), where(H−S) is the thickness of the spacer element. In this way, the thicknessof a back-to-back planar element and spacer element is H. The spacersprovide a minimum separation distance between all optical sensor layers.The wedges tilt the optical sensor layers into desired planes. Thematerials for the spacers and wedges should be thermally stable andincompressible but easily penetrable. Incompressibility is desirable sothat the geometry of the sensor structure is maintained as theprojectile passes through. Example materials include plastics(polycarbonates (e.g., Lexan®)), silicone gel compounds, and fiberreinforced and non-reinforced polyimide-based composite materials.

While the FIG. 2 structure illustrates one example of the orientationfor optical sensors, may other orientations are possible. With referenceto FIG. 2, the primary axis of the structure is the X axis because mostof the projectile movement is confined to this dimension. The Xdimension in the example structure is unique because the plane of thefirst optical sensor (40) corresponds to X=0 and therefore a pulse fromthis sensor corresponds directly to when the X dimension of projectileposition is equal to zero. No extra computations are required to discernthis, as it is a direct result of the geometry of the sensor structureand how the coordinate system was defined. The first and sixth opticalsensors in FIG. 2 (40,70) are parallel and their primary use is themeasurement of the X dimension of the projectile velocity. For the Y andZ dimensions in FIG. 2, projectile characterization is not asstraightforward. The reason for this is that the impact position in thefirst sensor (40) is not known apriori. For purposes of an opticalsensor structure according to the present invention, pairs of additionaloptical sensors should be positioned in at least two inclined planes foreach additional dimension of interest for the projectile parameters. Forexample, inclined sensors 50 and 55 in FIG. 2 are used to measure thetwo projectile parameters that are associated with the Y dimension,namely the impact location y₀ and the Y component of projectile velocityVy. Similarly, inclined sensors 60 and 65 are used to measure the Zdimension information. The specific structure illustrated in FIG. 2 isnot the only structure that could yield full three-dimensionalinformation regarding the projectile; however at least two planes areneed for each dimension of interest and they must be inclined withrespect to the primary axis of the structure if both impact position andthe velocity component in that particular dimension are desired. Inaddition, as noted herein, the last sensor (45), such as the seventhsensor is optional and intended to provide better accuracy by providingan independent way to measure the velocity attenuation factor. The useof the extra sensor to measure the velocity attenuation allows for thecomputation of the fragment parameters with confidence. Without theextra sensor, the fragment parameter computations can only be performedwith assumptions regarding the velocity attenuation, assumptions thatcould introduce measurement error. Obviously, the reference to theseventh sensor is with respect to the FIG. 2 structure. If, for example,basic optical sensor structure in accordance with the present inventionhas only four sensors, the optional sensor would be a fifth sensor.

As described with reference to the illustrative embodiment shown in FIG.1, the illustrated optical sensor includes five layers. Referring toFIG. 1, those layers include a transparent layer 20 also labeled as “T”in FIG. 1. The transparent layer 20 or T is sandwiched between tworeflective layers 15 and 25 that are also labeled as “R” in FIG. 1. Thereflective layers 15 and 25 are in turn sandwiched between two opaquelayers 10 and 30 which are also labeled as “O” in FIG. 1. The palindromestack-up of each optical sensor layer is thus ORTRO. As noted above, theopaque layers 10 and 30 function to prevent ambient light from enteringdevice. The reflective layers function to contain light within thetransparent layer 20. The transparent layer 20 couples the lightgenerated by the projectile into an attached optical fiber 35. Theoverall stack-up of an optical sensor structure isORTROSWORTROWSWORTROWSWORTROWSWORTROWSORTROSORTRO. This is a total of 49elements. An opaque outer jacket is also required around the overalloptical sensor structure to preclude ambient light from entering thesensor structure from the edges of the transparent layers of theindividual sensor elements. This can be made from the same materialsthat are used for layers 10 and 30 in the individual sensing elements.Optical fiber attachments to the transparent layers should be securedmechanically to prevent inadvertently dislodging the fiber. Efficientoptical coupling is achieved by inserting the optical fiber end directlyinto the transparent plane of each sensor. Optically clear epoxies canbe used to secure the attachment. Alternatively, the optical fibers maybe attached edgewise to the transparent planes; however, it is necessaryto scratch the outer surface of the fiber by sandblasting or othermethods to provide paths for the planar light to enter the fiber. Theedgewise attachment method offers advantages for routing the fibersalong unobtrusive paths back to the detectors; however, the signallevels are lower, all else being the same. Thus, this method may only beused if the projectile-induced signal levels are large enough to reachthe detector thresholds. Interlayer adhesives have not been addressed inthe above. The adhesives should have a uniform known thickness. It isalso preferable that they do not delaminate pieces of the structureunder the intended operational conditions. They are well known to thoseskilled in the art.

The following discusses some exemplary applications of the presentinvention.

Single Optical Sensor Layer Applications

A single optical sensor layer embodying the present invention can beused to detect projectiles from an explosive device that impact asurface. In many applications, it is desirable to know when projectilesfrom an explosive device penetrate at a particular location. Theplacement of a single optical sensor layer on a surface will allow forthe generation of an optical pulse when the projectile impacts and/orpenetrates the layer device. The placement of back-to-back layers of thesame layer device, with or without a spacer element between them, canprovide a rough measure of penetration speed. If it is known that theprojectile will penetrate normal to the surface of the two back-to-backlayers of the same layer device, then the stack up can be used tocompute projectile speed. Tiling of single optical sensor layers can beused to provide for impact coverage over a wider area. By offsetting twotiled layers from each other, additional spatial resolution can begained.

Other applications include: (1) detection of energetic particles thatare capable of generating an optical pulse signature, such asmicrometeorite detection; (2) detection of penetration caused by bulletsor other high-energy projectiles; and (3) impact detection caused by alocalized impulsive force on a surface. By using a material thatgenerates light on impact within any of all of the layers 15, 20, and25, the light could couple into the optical fiber 35, and indicate theapplication of an impulsive force. Examples of materials that can yieldflash augmentation can be readily suspended in particulate, filledbubbles, or microsphere encapsulation forms in the optically clearmedium include phosphorescent minerals (barium sulfide, calcium sulfide,and strontium sulfide) and chemical elements (phosphorous), combustiblemetals (magnesium), and reflective metal alloys (aluminum).

Multiple Optical Sensor Layer Applications

An optical sensor structure that includes multiple optical sensor layersembodying the present invention can be used to detect and characterizeprojectiles incident on a surface from some explosive device. In thecase of an explosion, the projectile characterization can allow foraccurate determination of the (1) location of the center of theexplosion, location of the impact point on a particular panel, e.g., 40,three-dimensional spatial velocity measurements, and measurement of thevelocity attenuation factor R. The exemplary optical sensor structuredevice shown in FIG. 2 includes seven optical sensor elements inaccordance with the present invention. The FIG. 2 structure is capableof resolving impact location and the speed and direction, i.e., thevelocity vector of a projectile relative to a coordinate system definedby the construction of the optical sensor structure such as shown inFIG. 2. The FIG. 2 structure is also capable of measuring the velocityattenuation factor associated with projectile penetration. If theinitiation time of the explosive device is also known, then thestructure is also capable of determining the source position of theprojectile at the initiation time. This has immediate application fortargets used in missile defense tests. In the case of fragmentingdevices, when the time of initiation is known, the FIG. 2 structure canbe used to compute the location of the fragmenting device relative tothe target vehicle. In the case of target damage projected by kineticencounter, the FIG. 2 device can be used to provide critically importanttrajectory data as well. These data can greatly enhance thepost-intercept lethality assessment process. The FIG. 2 structure canalso be used in live fire testing as a diagnostic tool to identify thecenter of an explosion.

Another example application is in forensic post-detonation bombcharacterization. In high threat locations for explosive devices, amultichannel optical sensor layer, such as shown in FIG. 2, could beinstalled in advance. If an explosion were to occur, the optical sensorstructure could provide valuable forensic evidence that could be used topiece together critical information such as the original location of thebomb and energy content. This information could help investigators tosolve crimes. It is particularly useful in that it is not necessary tohave the device available after a measurement has occurred. The datarecord that is transmitted from the device is sufficient to reconstructthe events and characterize the explosion. For example, a FIG. 2 typestructure could be used in airplanes to provide forensic evidence of anexplosive event if the data from the FIG. 2 structure was recorded inthe Flight Data Recorder. In this application, it would be veryimportant to protect the optical fiber that transmits the data to therecorder location.

A FIG. 2 type structure could also be used by bomb squads as a device tocharacterize a bomb at the time of detonation. Rather than simplydetonating a dangerous device, the structure could be used to providevaluable information to characterize the device, such as the mass ofprojectiles emanating from the bomb.

Another application is in determining the source of a gunshot. Theoptical sensor structure such as shown in FIG. 2 can be packaged into aportable system that would allow moving infantry to immediately resolvethe source position of a gunshot fired by a sniper and provide a measureof the bullet velocity that can be used to immediately help identify theweapon. In this application, it would also be necessary to accuratelyknow the location and orientation of the optical sensor structure at thetime of impact with respect to the coordinate system of interest, thebattlespace. The use of the audible sound from the shot could be usedwith the optical sensor structure data to quickly resolve theorigination point of the bullet. This information could then betransmitted to situational awareness framework and appropriate defensiveaction could be taken without delay. Such a system could be contained onthe outside of a soldier's pack, for example, and used to be able torapidly respond to a sniper attack.

The following provides an illustrative analytical solution fordetermining projectile parameters. Assume that a projectile penetratesan optical sensor structure such as shown in FIG. 2. The followinganalysis demonstrates how a six component temporal vector can be used,together with the structural parameters of the optical sensor structure,to determine the penetration location (y₀, z₀) in plane 1, which is theplane that optical sensor layer 40 is positioned and to determine thethree components of projectile velocity (V_(x), V_(y), and V_(z)). Thetemporal vector includes the penetration time associated with opticalsensors 1 through 6 (40, 50, 55, 60, 65, and 70) positioned in itscorresponding plane. Without loss of generality, we are free to definethe time when the projectile penetrates plane 1 as t₁=0, where plane 1is the plane in which optical sensor 40 is positioned. ThereforeX(t₁)=x₀=0. The parametric representation for the trajectory of theprojectile is given in equations (1) through (3).X(t)=V _(x) t  (1)Y(t)=y ₀ +V _(y) t  (2)Z(t)=z ₀ +V _(z) t  (3)This parametric representation assumes that the velocity attenuationfactor is equal to unity; the projectile passes through the sensorwithout slowing down. If this is the case, then the six componenttemporal vector is sufficient to uniquely resolve the projectile impactlocation and velocity components. Later in the analysis, a sensor in theseventh plane, 45, is used to be able to perform the same computationseven when R>1.

In the coordinate system of the optical sensor structure shown in FIG.2, the equations of the seven planes are in the form shown in equation(4).X+B _(j2) Y+B _(j3) Z=E _(j) j=1,2,3,4,5,6,7  (4)The coefficients B_(j2), B_(j3), and E_(j) are dependent on thegeometric parameters of optical sensor structure construction. A simpleconstruction is described that uses three geometric parameters L, H, andD. L is the width of the optical sensor structure in the Y and Zdimensions. H is the thickness of the spacer element less the thicknessof the optical sensor layer. D is the product of L and the tangent(A),where A is the wedge angle that is used to construct the wedge elementsshow in FIG. 3. With these definitions and the optical sensor structureconstruction defined, the equations for planes 1 through 6 (40, 50, 55,60, 65, and 70) are listed in equations (5) through (10).X=0 plane 1  (5)X+DY=(H+D)L plane 2  (6)X−DY=(2H+D)L plane 3  (7)X+DZ=(3H+3D)L plane 4  (8)X−DZ=(4H+3D)L plane 5  (9)X=(5H+4D)L plane 6  (10)The next step is to substitute the parametric equations for theprojectile into the X, Y, and Z variables in the planar equations. Thetime of penetration of plane j is denoted as t_(j). The new equationsare shown in (11) through (16).V_(x)t₁=0 plane 1  (11)V _(x) t ₂ +D(y ₀ +V _(y) t ₂)=(H+D)L plane 2  (12)V _(x) t ₃ −D(y ₀ +V _(y) t ₃)=(2H+D)L plane 3  (13)V _(x) t ₄ +D(z ₀ +V _(z) t ₄)=(3H+3D)L plane 4  (14)V _(x) t ₅ −D(z ₀ +V _(z) t ₅)=(4H+3D)L plane 5  (15)V _(x) t ₆=(5H+4D)L plane 6  (16)Equation (11) says that t₁=0. Equations (12) through (16) can beexpressed in the matrix form MP=Q, as shown in equation (17).$\begin{matrix}{{\begin{pmatrix}D & 0 & t_{2} & {Dt}_{2} & 0 \\{- D} & 0 & t_{3} & {- {Dt}_{3}} & 0 \\0 & D & t_{4} & 0 & {Dt}_{4} \\0 & {- D} & t_{5} & 0 & {- {Dt}_{5}} \\0 & 0 & t_{6} & 0 & 0\end{pmatrix}\begin{pmatrix}y_{0} \\z_{0} \\V_{x} \\V_{y} \\V_{z}\end{pmatrix}} = \begin{pmatrix}{\left( {H + D} \right)L} \\{\left( {{2H} + D} \right)L} \\{\left( {{3H} + {3D}} \right)L} \\{\left( {{4H} + {3D}} \right)L} \\{\left( {{5H} + {4D}} \right)L}\end{pmatrix}} & (17)\end{matrix}$And the solution for the projectile parameters P is found by inverting Mand multiplying by Q, equation (18).P=M ⁻¹ Q  (18)

In practice, the time vector is measured based on the optical pulseprovided to a computer from the fiber optic, such as 35, associated witheach of the six optical sensor layers of the FIG. 2 optical structure.Matrix M is then constructed based on the time vector. Then matrix M isinverted and matrix multiplied by Q for the solution P. The MATLAB codebelow, provides an exemplary solution embodying the above analysis for asimulated projectile solution.

Once P is known, then the projectile position can be computed for anytime given, assuming straight-line constant velocity motion of theprojectile. For a given time t_mark the position of the projectile canbe computed per equations (1) through (3) with t_mark substituted for t.This would allow, for example, the determination of the originationpoint of a projectile if the initiation time was known. In someapplications, the initiation time may be measured optically by usinganother optical fiber on the optical sensor structure shown in FIG. 2 todetect the light from the explosion. In other cases, such as for agunshot, the initiation time must be computed from the knowledge thatthe sound and the projectile must travel the same distance to theoptical sensor structure. If a sound transducer is located on plane 1 ofthe structure, the sound detection time t_(s) is known. This time willlikely occur after the projectile has already arrived at t=0. To computethe initiation time in this case, it is first necessary to compute thelocal sound speed, which is known to be a function of the airtemperature and pressure. Assuming these measurements are available atthe computer connected to the optical sensor structure, then the localsound speed S is known. Equation (19) then shows the equation forcomputing the bullet initiation time.t_mark=St _(s)/(S−√{square root over (V _(x) ² +V _(x) ² +V _(z) ²)})  (19)This value can then be substituted for t in equations (1) through (3) tocompute the spatial coordinates where the gunshot initiated relative tothe optical sensor structure. It the sensor was not secured to a fixedposition, it would also be necessary to have a record of the sensorlocation and orientation at the time of impact with respect to thebattlespace coordinate system if the additional information was to be ofuse since the sensor computations of the projectile parameters areperformed relative to the sensor coordinate system at the time ofimpact.

In some applications, fewer planes within the optical sensor structuremay be used if less information is needed. For example, those skilled inthe art will recognize that a four plane system would be sufficient toresolve V_(x), V_(y), and y₀ (assuming R=0) by employing an approachsimilar to that described above.

Handling Speed Attenuation

As a projectile passes through the sensor, it may experience speedattenuation as energy is transferred into the optical sensor structure.This results in a stretching of the time vector response. A method isdescribed here for correcting for this phenomenon by processing the timevector prior to performing the computation of P. The resultingcontracted time vector is the time vector that would have been measuredif no speed attenuation had occurred. The velocity attenuation parameterR is defined as the ratio of the input speed to the output speed, for asingle planar element, per equation (20). It is assumed that theinter-panel material slows the projectile by a negligible amount.R=In_speed/Out_speed  (20)A recursive relationship then exists that allows for the computation ofthe stretched time vector from the unstretched time vector, equation(21), where the variable r corresponds to the stretched time vector.r _(n) =r _(n−1)+(t _(n) −t _(n−1))R ^(n−1)  (21)

The solution to this recurrence relation provides a linear relationshipbetween the contracted time vector and the stretched time vector thatcan be expressed in matrix form Kt=r. Since the time of penetrationthrough the first panel is still equal to zero, only the timescorresponding to the penetration of planes 2 through 7 are relevant forthe computation of P; ie r₁=t₁=0. The full expression of this matrixequation is shown in equation (22). $\begin{matrix}{{\begin{pmatrix}R & 0 & 0 & 0 & 0 & 0 \\{R - R^{2}} & R^{2} & 0 & 0 & 0 & 0 \\{R - R^{2}} & {R^{2} - R^{3}} & R^{3} & 0 & 0 & 0 \\{R - R^{2}} & {R^{2} - R^{3}} & {R^{3} - R^{4}} & R^{4} & 0 & 0 \\{R - R^{2}} & {R^{2} - R^{3}} & {R^{3} - R^{4}} & {R^{4} - R^{5}} & R^{5} & 0 \\{R - R^{2}} & {R^{2} - R^{3}} & {R^{3} - R^{4}} & {R^{4} - R^{5}} & {R^{5} - R^{6}} & R^{6}\end{pmatrix}\begin{pmatrix}t_{2} \\t_{3} \\t_{4} \\t_{5} \\t_{6} \\t_{7}\end{pmatrix}} = \begin{pmatrix}r_{2} \\r_{3} \\r_{4} \\r_{5} \\r_{6} \\r_{7}\end{pmatrix}} & (22)\end{matrix}$Note that if R=1, then K is equal to the identity matrix and the timevector is not stretched. In actual application, the measured time vectorr must be contracted using the inverse transformation, equation (23)t=K⁻¹r prior to the computation of the parameter matrix P. R must beknown to be able to accomplish this.t=K ⁻¹ r  (23)

A method is described for computing R and hence the matrix K from theoriginal time vector. This is significant since R may vary from oneprojectile to the next. Even if R=1.001, the computed hit location andprojectile velocity will have significant error if the actual speedattenuation is not taken into account. Since stretched time vectors canhave computationally valid solutions for the projectile parameters, itis important that speed attenuation be known and the time vector iscontracted prior to the computation of the projectile parameters. Oneway to build the measurement of R into a sensor structure in accordancewith the present invention is to use a seventh plane (45) after thesixth sensor (70). The method here is to find the value of R that yieldsa contracted time vector and resulting V_(x) that is consistent with thesignal from the sensor in the seventh plane (45). The known spacingbetween the sixth and seventh sensors (70 and 45), HL, along with thetemporal relationship of their responses yields an independent measureof V_(x) at that point in the trajectory. Since the x component of thevelocity must have the same attenuation R, it is possible to compute asingle value of R that is consistent. Equation (24) expresses thenomenclature used in the following derivation and in the exemplaryMATLAB code listing.r _(ij) =r _(i) −r _(j)  (24)

Since the projectile must pass through six planes to get to the seventh,it experiences six speed reductions before it gets to the final, seventhsensor plane. This also holds true for each component of the velocityvector; therefore, an expression for V_(x) is shown in equation (25).HLR⁶ =V _(x) r ₇₆  (25)Similarly, if the projectile had not been retarded during passage,another expression can be written based on a contracted time when theprojectile would have reached the sixth sensor (70), equation (26).(5H+4D)L=V _(x) t ₆  (26)Solving both equations for V_(x) and equating them yields equation (27),where L cancels out.(5H+4D)t ₆ =HR ⁶ /r ₇₆  (27)The recurrence relation, equation (21), can be used to develop anexpression for t₆ in terms of the components of the stretched timevector, equation (28).t ₆ =R ⁻⁵ r ₆₅ +R ⁻⁴ r ₅₄ +R ⁻³ r ₄₃ +R ⁻² r ₃₂ +R ⁻¹ r ₂₁  (28)Substituting equation (28) into equation (27) yields a 5th orderpolynomial, equation (29) in R and the real solution is the R value asmeasured directly from the stretched time vector.−Hr ₂₁ R ⁵ −Hr ₃₂ R ⁴ −Hr ₄₃ R ³ −Hr ₅₄ R ² −Hr ₆₅ R+(5H+4D)r ₇₆=0  (29)This has been validated in the exemplary MATLAB code listing. Theindependent measure of R by the use of a seventh sensor results in muchgreater accuracy and potentially can be correlated to the caliber of aprojectile for a given sensor structure.Scaling of Time VectorsAs would be expected, the scaling of a time vector by a scalar quantityW results in computed velocity components that are scaled by W⁻¹ withimpact position unchanged.

Exemplary MATLAB code Listing % In a six sensor structure, fiveequations can be used by computing based on t=0 when fragment hits frontpanel of MPOPS % The equations directly yield fragment hit location atthe first plane and % velocity. Initial positions can then be computedbased on initiation % time. In real application, the initiation time maynot be available. % The following solution is not dependent oninitiation time knowledge for % The code checks if the temporal vectoris ordered % If the vector is ordered, the solution is found % If not,an error message is issued % % The ratio of input speed/output speed = R% A matrix K is used to contract the time vector prior to computing P %If R=1 (ideal case), then K is the identity matrix % % The code allowsthe use of a seventh sensor to compute R % from temporal measurements.The method requires the solution of a 5th % order polynomial. Byindependently measuring % R, the resulting projectile parameters aremore accurate. Also the % measurement of R provides additionalinformation about how the projectile % interacts with the optical sensorstructure. This additional information % might be sufficient to resolveweapon caliber or particle size. The % seventh sensor is in a plane thatis parallel to the sixth plane behind % an additional spacer element. Inthis % simulation, R is given to allow for computation of the retardedtime % vector. Then computation of R from the retarded vector provesthat a % measured retarded time vector will yield the same R directly.The % derivation of the 5th order equation requiring solution is beyondthe % scope of this comment. % % % Approach is to encode six planarequations in coordinate system (1st % equation is trial, x0=0); %Specify fragment parameters % Compute plane penetration times, assumingplane 1 is penetrated at t=0 % Back-compute fragment parameters frompenetration time vector % Then compare back-computed parameters tooriginal % This allows for proof of concept since single panel test hasalready % been performed % This will allow testing the effect ofdeceleration and panel % intolerances as well by interactively adjustingthe forward computed % penetration times and analyzing the effect onback-computed fragment % parameters % % Panel design parameters % %H=interpanel gap/L % D=percent depth change of wedge across panel width% L=panel width=panel height % Width is Y dimension % Height is Zdimension % Depth is X dimension % d=thickness of an individual POPSelement relative to L % R=panel speed reducing ratio; Input speed/Outputspeed = R for a plane % T=overall 6-DOF POPS thickness % clear all; %d=0.01; L=1; H=0.05; D=0.15; R=1.03; T=(5*H+4*D)*L % % For now it isassumed that D is part of interchannel gap % Later it may be necessaryto upgrade code % % Fragment parameter vector has six components % %x_init,y_init,z_init,vx,vy,vz % % x_init,y_init,z_init is initialfragment position % vx,vy,vz is fragment velocity vector % % units ofx_init, y_init, and z_init are panel widths, relative to coordinatesystem % in Figure illustrating the 6-DOF POPS % % units of vx, vy, andvz are panel widths per millisecond % % The supplied parameters for thesimulation are x_p1, y_p1, z_p1, t_(—) mark, vx, vy, and vz. % x_p1,y_p1, and z_p1 are the x,y,z components of the hit point % and t_mark isthe time of interest of the fragment relative to impact % time at p1.t_mark could be the initiation time or some other time of interest forthe fragment. % A negative t_mark value corresponds to pre-impactposition. % A positive t_mark value corresponds to post-impact position.% the vx, vy, and vz are the supplied fragment velocity components % (vx< > 0). vx can be negative and impact times are still computed relativeto impact % at p1 % x_p1=0; y_p1=0.5; z_p1=0.2; t_mark=0; vx=3; vy=0.2;vz=0.2; % % Compute the mark point based on the supplied simulationparameters % x_mark=x_p1+vx*t_mark; y_mark=y_p1+vy*t_mark;z_mark=z_p1+vz*t_mark; Fin=[x_mark y_mark z_mark vx vy vz]; % % Fsim isthe starting point of the fragment at the MPOPS. Fsim=[x_p1 y_p1 z_p1 vxvy vz]; % % Computed penetration times for planes 1 through 6 assumingK=1. % t1=0; t2=((H+D)*L−Fsim(1)−Fsim(2)*D)/(Fsim(4)+Fsim(5)*D);t3=((2*H+D)*L−Fsim(1)+Fsim(2)*D)/(Fsim(4)−Fsim(5)*D);t4=((3*H+3*D)*L−Fsim(1)−Fsim(3)*D)/(Fsim(4)+Fsim(6)*D);t5=((4*H+3*D)*L−Fsim(1)+Fsim(3)*D)/(Fsim(4)−Fsim(6)*D);t6=((5*H+4*D)*L−Fsim(1))/Fsim(4); t7=((6*H+4*D)*L−Fsim(1))/Fsim(4);t=[t1 t2 t3 t4 t5 t6 t7]; % % Check that temporal vector is ordered %s=sort(t)  %sorts in ascending order r=fliplr(s) %flips left to right %Perform computations iff temporal vector is ordered if (all(t == s) |all(t == r)) % % K is a matrix used to convert an unretarded time vectorto a retarded % time vector. It arises from a recurrence relationdocumented elsewhere % K is the identity matrix iff R=1 % K(1,:)=[R 0 00 0 0]; K(2,:)=[R-R{circumflex over ( )}2 R{circumflex over ( )}2 0 0 00]; K(3,:)=[R-R{circumflex over ( )}2 R{circumflex over( )}2-R{circumflex over ( )}3 R{circumflex over ( )}3 0 0 0];K(4,:)=[R-R{circumflex over ( )}2 R{circumflex over ( )}2-R{circumflexover ( )}3 R{circumflex over ( )}3-R{circumflex over ( )}4 R{circumflexover ( )}4 0 0]; K(5,:)=[R-R{circumflex over ( )}2 R{circumflex over( )}2-R{circumflex over ( )}3 R{circumflex over ( )}3-R{circumflex over( )}4 R{circumflex over ( )}4-R{circumflex over ( )}5 R{circumflex over( )}5 0]; K(6,:)=[R-R{circumflex over ( )}2 R{circumflex over( )}2-R{circumflex over ( )}3 R{circumflex over ( )}3-R{circumflex over( )}4 R{circumflex over ( )}4-R{circumflex over ( )}5 R{circumflex over( )}5-R{circumflex over ( )}6 R{circumflex over ( )}6]; % %Generate theretarded time vector r r = K*t(2:7)′; % Contract the retarded timevector tempt=inv(K)*r; t=[0 tempt′]; % solve 5th order polynomial for Rbased on retarded time vector r = [0 r′]; f=diff(r); rpoly=[−H*f(1)−H*f(2) −H*f(3) −H*f(4) −H*f(5) (5*H+4*D)*f(6)]; solution =roots(rpoly); R_comp=solution(5) R % Define the measurement matrix M andthe depth vector Q % M(1,:)=[ D   0 t(2)   D*t(2)   0 ]; M(2,:)=[−D   0t(3) −D*t(3)   0 ]; M(3,:)=[ 0   D t(4)   0   D*t(4) ]; M(4,:)=[ 0 −Dt(5)   0 −D*t(5) ]; M(5,:)=[ 0   0 t(6)   0   0 ]; % Q(1,1)=(H+D)*L;Q(2,1)=(2*H+D)*L; Q(3,1)=(3*H+3*D)*L; Q(4,1)=(4*H+3*D)*L;Q(5,1)=(5*H+4*D)*L; % % List times that fragment passes each plane,referenced to the first plane % Compute the Fragment Vector Output Foutand Compare to the Fragment Vector % Input Fin. The fragment parametersfp is the matrix product of the inverse of M times D % The first 2components of fp are the computed Yhit and Zhit values and the last 3components are the % computed fragment velocity components vx, vy, andvz. % Fout is then computed to compare with Fin % t r P=inv(M)*Q;%fragment parameters Hit=[0 P(1) P(2)] Vel=[P(3) P(4) P(5)]Inspeed=sqrt(P(3){circumflex over ( )}2+P(4){circumflex over( )}2+P(5){circumflex over ( )}2) Outspeed=Inspeed/R{circumflex over( )}6 Fin Fout=[t_mark*Vel(1) P(1)+t_mark*Vel(2) P(2)+t_mark*Vel(3)Vel(1) Vel(2) Vel(3)] save C:\MATLAB6p5\work\pops-output.txt t r HitInspeed Outspeed Fin Fout - ASCII else   disp(‘Scrambled timevector...multiple hit or data system error ’) end

FIG. 5 is a schematic block diagram of a detection system embodying thepresent invention with a single optical fiber transmitting an opticalsignal from an optical sensor to a corresponding detector. In FIG. 5,optical sensors embodying the present invention (75, 80, and 90) areconnected via respective individual optical fibers (95, 100, and 105) tocorresponding detectors (110, 115, and 120). The detectors 110, 115, and120 can comprise, for example, photodetectors. The detectors 110, 115,and 120 can provide, for example, optoelectronic conversion of theoptical signal detected on fiber optics 95, 100, and 105. The detectorscan also provide filtering and threshold detection of the electricsignal generated by the detectors. While not shown in FIG. 5, thedetectors are operatively coupled to a computer that receives the timepulses provided by the optical sensors 75, 80, and 90 and detectors 110,115, and 120. These time pulses can be processed in accordance with theabove equations and processing represented by the exemplary MATLAB code.

FIG. 6 is a schematic block diagram of a detection system embodying thepresent invention with a single optical fiber transmitting all opticalsensor signals to a single detector.

In FIG. 6, optical sensors 125, 130, and 135 are connected to an N-to-1optical connector, 155, via short or local optical fibers 140, 145, and150. As is known to those skilled in the art, the N-to-1 opticalconnector, 155, couples the light from each of the optical fibers, 140,145, and 150 into the optical fiber 160. The optical fiber 160 carriesthe optical signals to the detector 165, which is typically located asafe distance from the event being monitored by the optical sensors,such as an explosion. The detector 165 can comprise, for example, aphotodetector. The detector 165 can provide, for example, optoelectronicconversion of the optical signal detected on fiber optic 160. Thedetector can also provide filtering and threshold detection of theelectric signal generated by the detector. While not shown in FIG. 6,the detector 165 is operatively coupled to a computer that receives thetime pulses provided by the optical sensors 125, 130, and 135 anddetector 165. These time pulses can be processed in accordance with theabove equations and processing represented by the exemplary MATLAB code.

FIG. 7 is a schematic block diagram of a detection system embodying thepresent invention with a single optical fiber transmitting all opticalsensor signals to an array of detectors. The FIG. 7 system makes use ofdifferent light wavelengths provided by the optical sensors 170, 175,and 180. The light provided by the optical sensors 170, 175, and 180 iscoupled to an N-to-1 optical connector 200 via short or local fiberoptics 185, 190, and 195. As is known to those skilled in the art, theN-to-1 optical connector, 200, couples the light from each of the fiberoptics, 170, 175, and 180 into the fiber optic 240. The optical fiber240 carries the optical signals to the 1-to-N optical connector 205,which is typically located a safe distance from the event beingmonitored by the optical sensors, such as an explosion. As is well knownto those skilled in the art, the 1-to-N optical connector 205, couplesthe different wavelengths of light to the corresponding fiber optics210, 215, and 220. The detectors 225, 230, and 235 detect the lightcarried by the corresponding fiber optics 210, 215, and 220. As withFIGS. 5 and 6, the detectors 225, 230, and 235 can comprise, forexample, photodetectors that are sensitive to different wavelengths oflight. The detectors 225, 230, and 235 can provide, for example,optoelectronic conversion of the optical signal detected on thecorresponding fiber optics 210, 125, and 220. The detector can alsoprovide filtering and threshold detection of the electric signalgenerated by the detector. While not shown in FIG. 7, the detectors 225,230, and 235 are operatively coupled to a computer that receives thetime pulses provided by the optical sensors 170, 175, and 180 anddetectors 225, 230, and 235. These time pulses can be processed inaccordance with the above equations and processing represented by theexemplary MATLAB code.

1. A sensor structure comprising: a plurality of sensor membersrespectively oriented in corresponding planes, at least some of theplanes being oriented to intersect; and coupling members operativelycoupled to respective ones of the sensor members, wherein each of thesensor members further comprises: a light generator layer having top andbottom surfaces; opaque layers positioned over the top and bottomsurfaces; and wherein the coupling members are coupled to respectiveones of the light generator layers.
 2. A structure according to claim 1,wherein the light generator layer includes: an optically transparentmaterial having major surfaces; and reflective layers positioned overthe major surfaces.
 3. A sensor structure according to claim 2, whereinthe opaque layer include at least one of: optically opaque plastics,structural fiber reinforced composites, metals, and silicone moldingcompounds.
 4. A sensor structure according to claim 2, wherein theoptically transparent material includes at least one of: optically clearplastics and silicone-based molding compounds.
 5. A sensor structureaccording to claim 2, wherein the optically transparent materialincludes a transparent planar member.
 6. A sensor structure according toclaim 2, wherein the optically transparent material comprises a gas. 7.A sensor structure according to claim 2, wherein the reflective layersinclude at least one of: optically reflective plastics, metal alloyfilms, and polished metals.
 8. A sensor according to claim 2, whereinthe optically transparent material includes a flash augmentationmaterials, wherein the flash augmentation materials include at least oneof suspended in particulate, filled bubbles, or microsphereencapsulation comprising at least one of phosphorescent mineralsincluding barium sulfide, calcium sulfide, and strontium sulfide,phosphorous, combustible metals, and reflective metal alloys.
 9. Asensor structure according to claim 2, wherein the coupling memberincludes at least one optical fiber.
 10. A sensor structure according toclaim 1, wherein the plurality of sensor members comprises at least sixmembers.
 11. A sensor structure according to claim 1, wherein least twoof the sensor members are oriented in respective planes that areoriented to intersect along a first line, and at least two other of thesensor members are oriented in respective planes that are orientated tointersect along a second line.
 12. A sensor structure according to claim11, wherein the second line is orthogonal to the first line.
 13. Asensor structure according to claim 1, wherein the sensor memberscomprise electrical penetration sensors.